The present invention relates to hearing aids. In particular, the present invention pertains to switches for changing settings on a hearing aid having a digital signal processor (“DSP”) for processing the microphone sensed signal.
Hearing aids are electrical devices having a microphone to receive sound and convert the sound waves into an electrical signal, some sort of amplification electronics which increase and often modify the electrical signal, and a speaker (commonly called a “receiver” in the hearing aid industry) for converting the amplified output back into sound waves that can be better heard by the user. The electronic circuitry is commonly powered by a replaceable or rechargeable battery. In most modern hearing aids, an analog electrical output from the microphone is converted into a digital representation, and the amplification electronics include a DSP acting on the digital representation of the signal.
Hearing aids have long included settings which can be user-controlled to change the audio response parameters of a hearing aid, generally allowing the user to optimize the hearing aid for different varieties of listening situations. For instance, a first setting may be for normal listening situations, a second setting may be for listening in noisy environments, a third setting may be for listening to music, and a fourth setting may be for use with a telephone. Typically, the user can cycle through these settings (also called parameter sets or programs) using a switch on the hearing aid. Examples of the parameters that are adjusted between the various settings include volume, frequency response shaping, and compression characteristics.
The most common type of switch for cycling through hearing aid settings is a mechanical push button switch. The mechanical switch is usually located either on the body or the faceplate of the hearing aid in a position which the user can touch with a finger while wearing the hearing aid.
Mechanical switches, though simple, normally reliable and fairly low-cost, have their drawbacks. Due to the small size of the push button, the user may not always realize that the button has been pushed. To clearly indicate to the user that the push button has been activated, most hearing aids generate an audible tone. Despite the generated tone, however, most users still have a hard time locating the push button on the hearing aid because the push button is relatively small compared to the user's fingers. This drawback makes hearing aids with a push button hard to operate, especially for elderly users. As hearing aids become smaller and are positioned further in the user's ear canal, manipulation of the mechanical switch becomes more and more difficult for most users.
Additionally, push buttons located on the body or the faceplate of a hearing aid are susceptible to sweat and debris that can lead to switch failure. While switches are normally reliable, they include moving parts that can and do fail. Also, while the push button may be small relative to a user's finger tips, it still adds to the size of the hearing aid, thus making the hearing aid more visible and unattractive. While mechanical switches are relatively low cost, such as on the order of a few dollars, they still do contribute to the overall cost of the product.
Separate from the hearing aid industry, acoustic power-on switches for operating 120 Volt AC, plug-in appliances (lights, televisions, etc.) are well known in the U.S. by virtue of the advertising campaign of Joseph Enterprises for the CLAPPER device. See, for instance, U.S. Pat. Nos. 3,970,987, 5,493,618 and 5,615,271. In the most common CLAPPER device, the user brings his or her hands together in two loud claps, and the sound waves for the claps are received by a microphone and analyzed to assess when a user has intended to turn the appliance on or off.
Similarly, a wide variety of voice-activated switches have arisen which respond to vocal commands. Voice-activated commands have well documented problems in terms of cost, size, processing capabilities and accuracy.
While voice-activated and CLAPPER switches may be useful for appliances and other devices, similar types of switches have not found widespread use in hearing aids. Hearing aid users would often be unwilling to clap twice loudly or speak a command each time the user wants to change settings, including in the wide variety of locations where the hearing aid might be in use (such as during a music concert, in a quiet auditorium, etc.). Moreover, hearing aid users generally desire their hearing aid use to be as inconspicuous as possible. The costs of adding these types of switches to a hearing aid (not only monetary, but also processing/battery costs and size costs) have not been found commercially acceptable.
Several attempts have been made to replace the mechanical hearing aid switch with a processor-based switch based upon the microphone input but which avoids audible actuation. For instance, U.S. Pat. No. 6,748,089 to Harris et al. discloses a hearing aid switch which is intended to be actuated by the user placing his or her hand in a cupped position over the ear to attenuate the incoming audio signal. This solution has not found marketplace acceptance, likely due to its reliability. Audio signals witnessed by hearing aids naturally change amplitude on a moment to moment basis. It is very difficult to distinguish in a hearing aid processor when such amplitude changes occur due to hand placement over the ear from when such amplitude changes occur due to signal source variations.
As another example, U.S. Pat. No. 7,639,827 to Bachler discloses a hearing aid switch which is intended to be actuated by the user again placing his or her hand in a cupped position over the ear, this time to drive the hearing aid amplification circuit into an unstable, oscillation (feedback) condition. However, unstable oscillation often causes a loud whistling tone in hearing aids which users seek to avoid. Further, most users have many natural gestures and hand movements which place their hands adjacent their ears, and also place other items (telephones, hats, etc.) adjacent their ears. Additional complications arise in that users have differently shaped ears and different hearing aid placements (microphone locations) in their ears, meaning that the microphone response to a given input is not identical from user to user both located in the same room.
A good hearing aid switch should both avoid false positives, i.e., switching when the user has not intended to initiate the switch, and avoid false negatives, i.e., not recognizing each time the user has attempted to initiate the switching action. Until hearing aids are developed which can silently sense the brain waves of the user to determine when the user desires a switch between settings, better solutions are needed.